Investigators have studied the absorption of sound energy in toluene from 30 kc to 200 Mc in an effort to determine the causes of the excess absorption. The results to date have raised many puzzling questions. For example, Verma and Yeager (private communication) have reported a resonance peak at 50 kc, the existence of which is quite difficult to explain. R. T. Beyer reports a relaxation peak at 150 kc, the mechanism of which is not clear. We have made ultrasonicabsorption measurements in toluene using the reverberation method and the pulse method over a frequency range from 150 kc (overlapping Beyer's [J. Acoust. Soc. Am. 27, 1 (1955)] frequencies) to 55 Mc and a temperature range from 6° to 44°C. The high‐frequency attenuation is studied as a function of temperature, and it is found that the temperature dependence is different from that reported by G. S. Verma [J. Chem. Phys. 18, 1352 (1950)]. The results in the kilocycle region show that the absorption per wavelength has a resonance type peak at approximately 210 kc independent of temperature with a magnitude that increases with increase in temperature. The Q of this loss mechanism is about the same as the Q of the resonance type loss reported by Verma and Yeager in the 50‐kc region. The position and magnitude of the peak at 210 kc is unaffected by the introduction of ethyl alcohol as an impurity up to concentrations of 10% by volume.

The use of light diffraction for the measurement of the sound‐pressure amplitude and the waveform of ultrasonicwaves has been extended to the case of ultrasonic pulses. The method has been applied to transducercalibration in water at 5 Mc for pulses of 3 to 12 μsec duration, and compared with calibration by means of continuous waves. The distortion of the waveform in ultrasonic pulses of finite amplitude is demonstrated by measurements of the transducer voltage vs light intensity in the first diffraction orders. All measurements made with continuous waves and with pulses give approximately identical results.

An optical method is used to measure the energy ratio of reflected and incident ultrasonic waves at a liquid‐solid interface. The ultrasonic velocities in the solid are calculated from the angles of maximum reflection in the liquid.

Sound absorption and velocity measurements in fluorine at 28° and 102°C indicate vibrational relaxation times of 20.7 and 10.7 μsec for these two temperatures, respectively. The measurements were made inside a glass tube 1.73 cm in diameter using progressive waves. These results when combined with earlier results in the other halogens indicate certain changes which improve the accuracy of the Slawsky, Schwartz, and Herzfeld theory.

The vibration of circular plates with a large initial tension (or compression) is studied for the case of (a) simply supported and (b) clamped edges. The basic equation used is that of the Poisson‐Kirchhoff theory. Numerical results are given.

The load impedance of a generator or the radiation impedance of a transducer can be controlled by a second active generator coupled to the first generator by a transmission line. The primary control variables are the relative magnitude and phase of the signals in each generator. A load impedance of any magnitude and phase, including negative resistance, can be obtained. The second generator is used as an active reflector and absorber. The theory is applicable to the case where the generators are underwater soundtransducers and the line is a water‐filled tube.

The essential function of the optimum detector is that of applying linear mean‐square regression process to the output of the array and measuring the power in the residues thus formed. The elements required for instrumentation of the detector are deduced and numerical examples relating to specific array configurations are presented. At low frequencies the directivity pattern of the optimum detector is superdirective. There is strong evidence that this directivity pattern is the one having maximum directivity index.

In the frequency region below 1 kc, the effect of velocity inhomogeneities on acoustic propagation in the ocean will be negligible. In this frequency region, fluctuations in travel time and ray direction will be caused by scattering from rough boundaries. In this paper, the effect of boundary scattering on the resolution of ray paths is investigated. Using a simplified model of the process, a rough estimate of the spatial line broadening of a low‐frequency ray in the ocean is obtained.

The characteristics of a piston‐type transducer that must withstand varying hydrostaticpressures can be improved by mechanically preloading the assembled transducer prior to operation and by carefully matching the axial compliances of the individual elements. A simple analysis and some tests of an experimental preloaded transducer are described, and the particular advantages of conical disk springs as transducer isolators are discussed.

Acoustical pulses of variable length and repetition rate are generated by an electronic system composed of instruments which are commercially available, except for a gate unit. The system is designed to permit acoustic transmission and reflection experiments in a controlled water medium within the confines of a laboratory‐size wooden tank. Pulses of sine wave between 60 kc and 1 Mc are used. An acoustical source constructed of a barium‐titanate spherical cap generates an acoustical pressure field as high as 2.1×104 μbar (86.7 db re 1 μbar at 1 m) at 230 kc at a distance of 1 m which is sensed by miniature hydrophones with lead titanate‐zirconate disk elements as small as 0.063 by 0.009 in. The ceramic is enclosed by metal to overcome problems encountered previously with waterproof coatings incapable of keeping water from the ceramic for long periods of immersion. Pressure sensitivity of the probe hydrophone with preamplifier (49.6‐db gain) is 10.3×10−6 v/μbar (−99.8 db re 1 v/μbar) at 230 kc.

A group of hydrophone elements uniformly and closely spaced along a straight line is used to measure the angle of arrival of sound waves. By sampling the outputs of these elements rapidly and in succession, one simulates single hydrophone moving relative to the sound waves. The signal measured at the output has a frequency given by the Doppler equation , where f0 is the frequency of the sound in the water, α is the ratio of the scanning speed to the speed of sound, and θ is the bearing angle desired. The theoretical results expected along with the experimental measurements which confirm the theory and a description of the equipment used are included.

It was found that the scanned system simulates almost exactly a single moving point hydrophone, and the Doppler equation was found to hold. Pure tones and narrow‐band noise signals are shifted in frequency. The angular resolution was found to be equal to the ratio of the wavelength of the sound to the component of the hydrophone length normal to the direction of sound propagation.

The problems associated with determining the angular distribution of continuous and discrete noise sources by means of a linear additive array are discussed. A spatial frequency analysis shows that an array acts as a low‐pass filter in the spatial frequency domain and hence cannot distinguish between spatial‐noise distributions whose spatial spectra differ outside the spatial bandwidth of the array. It is shown that smoothing due to side‐lobe response results in a large reduction in the ability of an array to measure accurately peaks in the angular distribution.

Equations are derived to describe an underwater soundtransducer consisting of an acoustical transmission line coupled to a low‐pass electrical transmission line. If the two transmission lines have the same phase velocity, the energy of a wave is transferred cyclically from one line to the other as a function of line length; a reversible transducer with a low Q, high efficiency, and essentially constant resistive impedance is thereby achieved. Theory and four proposed designs are described.

The sound fields resulting from a plane wave incident on a spherical elastic shell are found. Both the internal and external fields due to the shell are considered and compared with well‐known results. The Rayleigh limit is discussed, and it is found that the external field is similar to that produced by a rigid sphere but with more complicated coefficients. The internal field is of a complicated nature but reasonable to consider for numerical computation. The sound fields for a hemispherical shell mounted on a rigid medium are obtained by the image method. Numerical results for the sound intensity at the center of the hemisphere are presented for various elastic materials.

The ability of subjects to judge the distance of the source of an unfamiliar sound was studied. It was found that distance judgments on the first trial were unrelated to actual distance. With further trials valid distance judgments became possible.

A transducer consisting of a barium‐titanate bilaminate‐strip mass loaded at the ends was found to have a resonant frequency in range 200 to 1700 cps. Comments are made on some of the electrical and mechanical parameters of this composite transducer.

Frequency analysis was made of vowelsounds produced after inhaling a high concentration of helium. Comparison of helium vowels with normal vowels shows an increase in the component frequencies. The formant ratios are found to remain nearly constant. A slight increase in fundamental frequency was observed, but this is postulated to be due to physiological rather than acoustic effects. The effective change in the velocity of sound in the vocal cavity during a helium utterance is considered.

The vibrational relaxation in nitrogen and oxygen, both pure and with admixtures, has been measured with a high‐pressure Kundt's tube. Pure nitrogen relaxes at f0/p of 1 cps/atm, at 203°C; oxygen at 90 cps/sec at 50°C.

Bulk viscosity and ultrasonicabsorption coefficients for carbon tetrachloride and chloroform at 20°C, 1 atm, have been recalculated in order to correct an earlier result which has been modified more recent work. The changes increase the vibrational relaxation contribution to the absorption by a factor of order unity, while the structural contributions, resulting from relaxation of the distribution of free volume, are left unchanged. New values for tetrachloride and chloroform, respectively, are: for bulk viscosity 0.2729 and 0.2934 poise; for 2α/ν2, the intensity absorption divided by the sound frequency squared, 8.84×10−15 and 7.88×10−15 sec2/cm. This represents an improvement, which is not very significant, in the agreement with experiment.